Metal polishing composition

ABSTRACT

An object of the present invention is to provide a metal polishing composition which can polish a metal such as Cu and Ta at a high speed, has a higher efficiency of washing for a hydrophobic low dielectric constant film, and is excellent stability without precipitation of a polishing particle during storage (excellent in stability for storing). The object is achieved by a metal polishing composition comprising an anionic surfactant having 2 or more anionic functional groups in a molecule, a polishing abrasive, an inorganic salt, and water.

FIELD OF THE INVENTION

[0001] The present invention relates to a metal polishing composition.

BACKGROUND OF THE INVENTION

[0002] Recently, for polishing the surface of a semiconductor substrate, chemical mechanical polishing (hereinafter, abbreviated as CMP in some cases) has been mainly used.

[0003] On the other hand, currently, from the viewpoint of high performance of LSI, a wiring material is changed from Al to Cu having a low electric resistance, and an insulating film between wirings is changed from a silicon oxide film to a low dielectric constant film having a lower dielectric constant. Further, it is being studied to form a wiring structure in which a barrier film composed of Ta or TaN for preventing Cu from diffusing into a low dielectric constant film is formed between Cu and a low dielectric constant film. With change in such the wiring material, low dielectric constant film and barrier film material, there is desired a metal polishing composition which can polish these wiring at a high speed, and can be used in CMP having high efficiency of washing on the surface of a substrate after polishing.

[0004] For example, there are proposed a metal polishing composition containing metal oxide such as silicon dioxide or silicon nitride as a polishing abrasive, and an ammonium compound such as ammonium nitrate as an inorganic salt (JP-No.10-310766A), and a metal polishing composition containing a silicon dioxide particle as a polishing abrasive, a first surfactant, and a second surfactant (JP-A No.2002-155268). The efficiency of washing for a low dielectric constant film of metal polishing agent described in JP-A No.10-310766 is insufficient and, a rate of polishing a metal such as Ta of the metal polishing agent described in JP-A No.2002-155268 is insufficient, and its stability for storing is insufficient.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide a metal polishing composition which can polish a metal such as Cu and Ta at a high speed, has a higher efficiency of washing for a hydrophobic low dielectric constant film, and is excellent stability without precipitation of a polishing abrasive during storage (excellent in stability for storing).

[0006] The present inventors intensively studied and, as a result, found that a metal polishing composition comprising an anionic surfactant having 2 or more anionic functional groups in a molecule, a polishing abrasive and an inorganic salt can polish a metal such as Ta at a high speed, and is excellent in stability for storing and efficiency of washing. Further, the present inventors found that polishing rate or stability for storing is further improved by further inclusion of a nonionic surfactant, and completed the present invention.

[0007] That is, the present invention provides a metal polishing composition comprising an anionic surfactant having 2 or more anionic functional groups in a molecule, a polishing abrasive, an inorganic salt, and water.

THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

[0008] The present invention will be illustrated in detail below.

[0009] The anionic surfactant used in the present invention contains 2 or more anionic functional groups in a molecule.

[0010] As used herein, the anionic functional group is a group which is dissociated in water and exhibits anionic property, and examples include a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, a carboxylic acid group, and salts of these functional groups.

[0011] The anionic surfactant used in the present invention is a surfactant containing 2 or more of the aforementioned anionic functional groups in a molecule, and may contain a functional group other than the anionic functional group, provided that the surfactant has negative charge in water, as a whole.

[0012] Examples of the anionic surfactant having 2 or more anionic functional groups in a molecular structure include alkylene disulfonic acid or alkylene disulfonate such as alkylene disulfonate disodium salt, arylene disulfonic acid or arylene disulfonate such as arylene disulfonate disodium salt, naphthalene disulfonic acid formalin condensate or naphthalene disulfonic acid formalin condensate salt such as naphtalene disulfonic acid formalin condensate disodium salt, phenol disulfonic acid formalin condensate in which X is hydrogen in the following formula (A) and phenol disulfonic acid formalin condensate salt such as phenol disulfonic acid formalin condensate disodium salt in which X is sodium in the following formula (A), and phenylphenol disulfonic acid formalin condensate in which X is hydrogen in the following formula (B) and phenylphenol disulfonic acid formalin condensate salt such as phenylphenol disulfonic acid formalin condensate disodium salt in which X is sodium in the following formula (B).

[0013] (X is hydrogen or alkali metal)

[0014] (X is hydrogen or alkali metal)

[0015] From the viewpoint of stability for storing of the resulting polishing composition, a preferable anionic surfactant used in the present invention is an anionic surfactant further having an ether linkage in a molecule. Examples of the anionic surfactant containing an ether linkage together with 2 or more anionic functional groups in a molecular structure include alkyl diphenyl ether disulfonic acid, alkyl diphenyl ether diphosphonic acid, alkyl diphenyl ether dicarboxylic aicd and salts thereof.

[0016] Among them, alkyl diphenyl ether disulfonic acid or a salt thereof is preferable. For example, dodecyl diphenyl ether disulfonic acid disodium salt, dodecyl dipheny ether disulfonic acid diammonium salt, and dodecyl diphenyl ether disulfonic acid ditriethanolamine salt are preferable.

[0017] These anionic surfactants may be used alone or in combination of 2 or more.

[0018] The polishing abrasive used in the present invention may be any of an inorganic particle and an organic particle. Examples of the inorganic particle include particles containing, as a main component, metal oxide such as silicon dioxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide and manganese dioxide. Among them, silicon dioxide is preferable, and fumed silica and colloidal silica are more preferable. From the viewpoint that during storage of the resulting metal polishing composition, precipitation is suppressed, particle diameters are uniform, and scratch on the surface of Cu or a low dielectric constant film is suppressed, colloidal silica is further preferable.

[0019] The organic particle is a particle containing an organic polymer compound as a main component, and examples include an organic polymer compound such as a methacrylic resin such as PMMA, a phenol resin, a melamine resin, a polystyrene resin and a polycarbonate resin, a vinyl compound polymer obtained by emulsion polymerization, and an ion exchange resin and a chelate resin having ability to adsorb a particular metal. Among them, from the viewpoint that polishing speed for a wiring, a low dielectric constant film and a barrier film can be controlled, an ion exchange resin and a chelate resin which adsorbs a metal such as Cu and Ta are preferable.

[0020] From the viewpoint of suppression of occurrence of scratch on the surface after polishing, an average particle diameter of a polishing particle is preferably 10 μm or smaller, more preferably 1.0 μm or smaller.

[0021] In addition, from the viewpoint of a polishing rate, an average particle diameter is more preferably 0.005 μm or larger.

[0022] Polishing abrasive having a uniform particle diameter may be used, or polishing particles having different average particle diameters may be used by mixing them. For example, a mixture of polishing particle having an average particle diameter of 0.1 μm and polishing particle having an average particle diameter of 0.1 μm may be used.

[0023] As the inorganic salt used in the present invention, a salt of an inorganic acid such as nitric acid, phosphoric aicd, hydrochloric acid and sulfuric acid, with any one of alkylammonium hydroxide, ammonia, alkylamine, alkanolamine and hydroxylamine is preferable.

[0024] Examples of alkylammonium hydroxide include tetramethylammonium hydroxide and tetraethyl ammonium hydroxide, examples of alkylamine include methylamine, ethylamine, propylamine and butylamine, examples of alkanolamine include monoethanolamine, diethanolamine, triethanolamine, and 2-(2-aminoethoxy) ethanol, and examples of hydroxylamine include hydroxylamine, and N,N-diethyl hydroxylamine.

[0025] Among these inorganic salts, nitrate is preferable. Examples of nitrate include tetramethylammonium hydroxide nitrate, ammonium nitrate, monoethanolamine nitrate, and hydroxylamine nitrate. Among them, ammonium nitrate is preferable.

[0026] These inorganic salts may be used alone or in combination of 2 or more. The inorganic salt may be prepared by mixing the aforementioned inorganic acid with any one of alkylammonium hydroxide, ammonia, alkylamine, alkanolamine and hydroxylamine, or a commercially available inorganic salt may be used as it is.

[0027] From the viewpoint of improvement in a polishing speed to a metal film such as a barrier metal film of Ta or the like, ammonium nitrate is preferable.

[0028] The metal polishing composition of the present invention may contain an organic acid or a salt thereof in addition to the aforementioned inorganic acid. Examples of the organic acid include carboxylic acid such as acetic acid, citric acid, lactic acid, malonic acid, tartaric acid, succinic acid, oxalic acid, amino acid, n-nonanoic acid, n-decanoic acid, n-octanoic acid, 2-ethylhexanoic acid, 2-methylheptanoic acid, 2-n-propyl-n-valeric acid, 2,2-dimethyl-n-valeric acid, n-heptanoic acid, 2-methylhexanoic acid, 5-methylhexanoic acid, t-butylacetic acid, n-hexanoic acid, 2,2-dimethyl-n-butyric acid, 3,3-n-butyric acid, 2-methyl-n-valeric acid, 3-methyl-n-valeric acid, 4-methyl-n-valeric acid, 2-methyl-n-butyric acid, 2-ethyl-n-butyric acid, isovaleric acid, DL-2-methylbutyric acid, pivalic acid, n-valeric acid, and n-butyric acid. Organic acids which are generally commercially available may be used.

[0029] Among these organic acids, from the viewpoint of improvement in efficiency of washing to a metal film, lactic acid, tartaricacid, succinic acid, oxalic acid, n-octanoic acid, 2,2-dimethyl-n-valeric acid, n-heptanoic acid, 5-methylhexanoic acid, t-butylacetic acid, n-hexanoic acid, 2,2-dimethyl-n-butyric acid, and 2-methyl-n-butyric acid and salts thereof are preferable. Examples of the salt include tetramethylammonium hydroxide salt, ammonium salt, monoethanolamine salt, and hydroxylamine salt. Among them, ammonium salt is particularly preferable. Most preferable is ammonium oxalate.

[0030] These organic acids may be used alone or in combination of 2 or more.

[0031] The metal polishing composition of the present invention may contain a nonionic surfactant.

[0032] Examples of the nonionic surfactant used include nonionic surfactants which are contained in a conventional metal polishing agent. For example, a nonionic surfactant represented by the following formula (I) is preferable:

Y—O—(C_(a)H_(2a)O)_(b)—(C_(x)H_(2x)O)_(y)—Z  (I)

[0033] (wherein a, b, x and y are independently a positive integer, and Y and Z are independently a hydrogen atom or a hydrocarbon group having a carbon number of from 9 to 19).

[0034] When one or both of Y and Z is (are) represented by a hydrocarbon group, the hydrocarbon group is preferably a saturated hydrocarbon group. The number of carbons in the hydrocarbon group is from 9 to 19, preferably from 9 to 12, more preferably from 10 or 12.

[0035] In the formula (I), x and y represent a positive integer, and x and a may be different or the same. From the viewpoint of solubility in water, x is preferably 10 or smaller, more preferably 5 or smaller. And, x is preferably 3 or larger, more preferably 3. From the viewpoint of wettability between a low dielectric constant insulating film described below, y is preferably 10 or smaller, more preferably 5or smaller. Usually, y is 1 or larger.

[0036] a is from 2 to 5, preferably from 2 or 3, more preferably 2. From the viewpoint of solubility in an aqueous solution, b is preferably 4 or larger, more preferably 5 or larger. From the viewpoint of wettability between a low dielectric films having the hydrophobic surface, 20 or smaller is preferable, 10 or smaller is more preferable.

[0037] Examples of these nonionic surfactants include polyoxyethylene polyoxypropylene decyl ether, polyoxyethylene polyoxypropylene lauryl ether, polyoxyethylene polyoxypropylene cetyl ether, polyoxyethylene polyoxypropylene stearyl ether, and polyoxyethylene polyoxypropylene oleyl ether. Among them, polyoxyethylene polyoxypropylene decyl ether, and polyoxyethylene polyoxypropylene lauryl ether are preferable.

[0038] The case where a is equal to x (a=x) in the aforementioned formula (I) is represented by the following formula (II):

Y—O—(C_(m)H_(2m)O)_(n)-Z  (II)

[0039] (wherein m and n are the same or different and are a positive integer, and Y and Z are as defined above)

[0040] In the formula (II), m is 2 to 5, preferably 2 or 3, more preferably 2. From the viewpoint of solubility in an aqueous solution, n is preferably 4 or larger, more preferably 5 or larger. From the viewpoint of wettability between a hydrophobic film, 20 or smaller is preferable, 10 or smaller is more preferable.

[0041] As the nonionic surfactant represented by the formula (II), for example, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether are better. Among them, polyoxyethylene decyl ether, and polyoxyethylene lauryl ether are preferable.

[0042] One or two or more of the aforementioned nonionic surfactants may be used. When two or more kinds are used, it is preferable that at least one kind is the nonionic surfactant represented by the aforementioned formula (II).

[0043] The metal polishing composition of the present invention may contain other components such as a corrosion inhibitor, an oxidizing agent, and an antifoaming agent.

[0044] Examples of the corrosion inhibitor include corrosion inhibitors which are generally used, such as azoles such as 1,2,3-benzotriazole, o-tolyltriazole, m-tolyltriazole, p-tolyltriazole, carboxybenzotriazole, 1-hydroxybenzotriazole, nitrobenzotriazole, and dihydroxypropylbenzotriazole; mercapto compounds such as thioglycolic acid, thiodiglycol, thioglycerol, 2-mercaptoimidazoline, 2-mercaptoethanol, and mercaptopropionic acid; and aromatic hydroxy compounds such as sugar alcohols such as mannitol and glucose, catechol, and pyrogallol. Among them, preferable are 1,2,3-benzotriazole and benzotriazole derivatives.

[0045] These corrosion inhibitors may be used alone or in combination of two or more. By inclusion of these corrosion inhibitors, there is a tendency that scratch and dishing are prevented from occurring on the surface after polishing.

[0046] From the viewpoint of further improvement in a polishing rate, the metal polishing composition of the present invention may contain an oxidizing agent.

[0047] Examples of the oxidizing agent include hydrogen peroxide, iodic acid, and iodate. Hydrogen peroxide is particularly preferable.

[0048] These oxidizing agents maybe used alone or in combination of two or more.

[0049] Examples of the antifoaming agent include an emulsifying agent and a water-soluble alcohol, such as various emulsifying agents such as polyether-type, special ester-type of trade name Adecanol LG-135 (manufactured by ASAHI DENKA Co., Ltd.), emulsion-type, silicon-based emulsion-type, special nonion-type of trade name Adecanol LG-674 (manufactured by ASAHI DENKA Co., Ltd.), and silicone-type, as well as water-soluble alcohols which are generally known to suppress foamability, such as methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-l-propanol, and 2-methoxyethanol.

[0050] The metal polishing composition of the present invention comprises the aforementioned polishing abrasive, inorganic salt, anionic surfactant and water. Further, an oxidizing agent, a corrosion inhibitor, and an antifoaming agent are added thereto as necessary.

[0051] A total amount of the polishing abrasive, the inorganic salt and the anionic surfactant in the metal polishing composition is usually from 0.1% by weight to 40% by weight, and water is from 60% by weight to 99.9% by weight. When other components such as the oxidizing agent, the corrosion inhibitor and the antifoaming agent are added, a total amount thereof is usually from 0.001% by weight to 15% by weight in the metal polishing composition.

[0052] Among a total amount of the polishing abrasive, inorganic salt and the anionic surfactant, a content of the polishing abrasive is from 0.05% by weight to 50% by weight, preferably from 0.12% by weight to 50% by weight. A content of the inorganic salt is from 0.01% by weight to 25% by weight, preferably from 0.25% by weight to 25% by weight, and a content of the anionic surfactant is from 0.001% by weight to25% by weight, preferably from 0.25% by weight to 25% by weight.

[0053] When the metal polishing composition contains the aforementioned nonionic surfactant, a total amount of the anionic surfactant and the nonionic surfactant is preferably in the same range as that of the aforementioned content of the anionic surfactant. It is preferable that, among a total amount of the anionic surfactant and the nonionic surfactant, at least 50% by weight or larger is the anionic surfactant. A ratio of the anionic surfactant and the nonionic surfactant is preferably in a range of 1:0.01 to 1:1.

[0054] When the metal polishing agent of the present invention contains an organic acid, content thereof is usually from 0.001 to 10% by weight in the metal polishing composition.

[0055] When other components such as the oxidizing agent, the corrosion inhibitor and the antifoarming agent are contained, a content of these components is such that the oxidizing agent is usually from 0.1 to 15% by weight, and the corrosion inhibitor is usually from 0.01 to 5.0% by weight in the metal polishing composition.

[0056] When the aforementioned polishing abrasive, inorganic salt, anionic surfactant and water and, further, other components such as the oxidizing agent, the corrosion inhibitor and the antifoaming agent are added, the order of adding them is not particularly limited. For dispersing them, a homogenizer, an ultrasound, a wet medium mill or the like are used.

[0057] A pH of the metal polishing composition of the present invention is preferably 3 to 12, more preferably 3 to 9, further preferably 7 to 9. A pH of the metal polishing composition is adjusted by adding an inorganic acid or an organic acid, an inorganic base such as alkali and ammonium, or an organic base such as organic amine after the aforementioned respective components are mixed. Examples of the inorganic acid include nitric acid, phosphoric acid and sulfuric acid, examples of the inorganic base include ammonium hydroxide, and examples of the organic base includes amines. It is preferable that these are free from a metal ion.

[0058] In addition, when the metal polishing composition of the present invention contains an oxidizing agent, an oxidizing agent is preferably mixed into the composition when polishing is conducted.

[0059] It is suggested that a solution having the aforementioned each component with the high concentration may be prepared, and this may be used by diluting with water when polishing is conducted.

[0060] The metal polishing composition of the present invention is suitably used for polishing the surface of a semiconductor substrate on which any one of a low dielectric constant film, a Cap layer film which is a protecting film for a low dielectric constant film, an insulating film utilized as an interlayer insulating film between wirings, or the like is exposed. Further, the composition is also suitably used for polishing the surface of a semiconductor substrate on which a low dielectric constant film, a Cap layer film, an interlayer insulating film, a Cu wiring film, a barrier Ta or TaN film and the like are exposed.

[0061] Examples of the low dielectric constant film and the protecting film for the low dielectric constant film include inorganic films such as FSG (F-containing SiO₂), SiOC (carbon-containing SiO₂), SiON (N-containing SiO₂), SiC, SiN and SiCN which are formed by a CVD method, polyorganosiloxane films such as MSQ (methylsylsesquioxane), HSQ (hydrogensylsesquioxane) and MHSQ (methylated hydrogensylsesquioxane) which are formed on a substrate by coating and firing, aromatic films such as PAE (polyaryl ether) and BCB (divinylsiloxane-bis-benzocyclobutene), and organic films such as Silk and porous Silk.

[0062] Examples of the interlayer insulating film between wirings to be polished by the metal polishing composition of the present invention include a CVD series SiO₂ film which is formed using tetraethoxysilane (TEOS) or silane gas, aHDP-SiO₂ film utilizing high density plasma, and a BPSG film in which a SiO₂ film is doped with B or P, and the like.

[0063] The composition of the present invention is suitable for polishing a surface having Cu as a wiring material for a semiconductor device such as LSI, Ta or TaN as a metal used in a barrier film, and a low dielectric constant film having the hydrophobic surface having deteriorated wettability with water as an insulating film between wirings, or a Cap layer film having the hydrophobic surface formed on a low dielectric constant film for protecting the low dielectric constant film, or a surface on which the above films is exposed during polishing treatment.

EXAMPLES

[0064] The present invention will be explained below by way of Examples, but the present invention is not limited by them.

Example 1 Preparation of Composition

[0065] To 0.3% by weight of silica, 1.0% by weight of ammonium nitrate, 1.0% by weight of diammonium dodecyldiphenyletherdisulfonate, 4% by weight of hydrogen peroxide and 0.2% by weight of benzotriazole was added water to a total of 100% by weight, and the materials were mixed. Nitric acid was added to the mixture to adjust to pH 4 (hereinafter, this was referred to as composition 1).

Example 2

[0066] A composition was prepared according to the same manner as that of Example 1 except that 0.1% by weight of polyoxyethylene lauryl ether was further added to the composition 1 to a total of 100% by weight, and the materials were mixed (hereinafter, this was referred to as composition 2).

Example 3

[0067] A composition was prepared according to the same manner as that of Example 1 except that 0.1% by weight of polyoxyethylene polyoxypropylene lauryl ether was added to the composition 1 to a total of 100% by weight, the materials were mixed, and then, ammonium hydroxide was added to the mixture so as to give pH 8.5 (hereinafter, this was referred to as composition 3).

Example 4

[0068] A composition was prepared according to the same manner as that of Example 2 except that 0.04% by weight of ammonium oxalate was further added to the composition 2, the materials were mixed to a total of 100% by weight, and then, ammonium hydroxide was added to the mixture so as to give pH 8.5 (hereinafter, this was referred to as composition 4).

Comparative Example 1

[0069] A composition was prepared according to the same manner as that of Example 1 except that dibutylnaphthalene sulfonate having only one anionic functional group was used as an anionic surfactant in place of diammonium dodecyl diphenyl ether disulfonate (hereinafter, this was referred to as comparative composition 1).

Comparative Example 2

[0070] A composition was prepared according to the same manner as that of Comparative Example 1 except that polyoxyethylene β-naphthyl ether sulfate ester sodium salt was used in place of dibutylnaphthalene sulfonate salt (hereinafter, this was referred to as comparative composition 2).

Comparative Example 3

[0071] A composition was prepared according to the same manner as that of Comparative Example 1 except that polyoxyethylene tridecyl ether sulfate ester sodium salt was used in place of dibutylnaphthalene sulfate (hereinafter, this was referred to as comparative composition 3).

Comparative Example 4

[0072] A composition was prepared according to the same manner as that of Example 1 except that a surfactant was not added (hereinafter, this was referred to as comparative composition 4).

Comparative Example 5

[0073] A composition was prepared according to the same manner as that of Example 1 except that a surfactant and ammonium nitrate were not added (hereinafter, this was referred to as comparative composition 5).

Experimental Example 1

[0074] Using the compositions 1, 2, 3 and 4, and the comparative compositions 1, 2, 3, 4 and 5, stability for storing, polishing rate, and efficiency for removing polishing particle adhered to a low dielectric constant film, a Cu film and a Ta film after completion of polishing were estimated.

[0075] [Polishing Conditions]

[0076] Polishing machine: Leaf-type CMP apparatus CMS-200M (manufactured by NuFlare Technology Inc.)

[0077] Pad:-polyurethane type

[0078] Rotation number of pad surface plate: 78 rpm

[0079] Rotation number of stage for holding wafer to be polished: 75 rpm

[0080] Polishing pressure: 15 KPa

[0081] Polishing slurry flow rate: 150 ml/min

[0082] Washing step: Roll brush washing, pencil brush washing, megasonic washing, and spin drying were performed in this order using ultrapure water.

[0083] [Measurement of Ta Film Polishing Rate]

[0084] A Ta film was made on a Si wafer using a sputtering method, and this film was used as a wafer to be polished to perform polishing according to the aforementioned polishing conditions. Before and after polishing, a thickness of a film was measured with an electron microscope. A polishing rate was obtained by dividing a difference in film thickness before and after polishing by a polishing time.

[0085] [Calculation of Particle Removal Rate]

[0086] Using a low dielectric constant film (SiOC film) made on a Si wafer by a CVD (Chemical Vapor Deposition) method, a Cu film made on a Si wafer by a plating method, and a Ta film made on a Si wafer by a sputtering method as a wafer to be polished, polishing was performed according to the aforementioned polishing conditions, to adhere a polishing particle onto the film. Before and after washing, the number of adhered particles having a particle diameter of 0.2 micron or more was measured with a particle measuring apparatus (WM-1500 (manufactured by TOPCON CORPORATION)) on a wafer. From the numbers of adhered particles before and after washing, a rate of particles removed by washing was calculated according to the following equation.

[0087] Method of calculating rate of removed particles Rate  of  removed  particles  (%) = (1 − (number  of  adhered  particles  after  washing)/(number  of  adhered  particles  before  washing)) × 100

[0088] The number of particles derived from the metal polishing agent on a low dielectric constant film before washing was about 10000 to 12000.

[0089] [Estimation of Stability for Storing]

[0090] In the compositions 1, 2, 3 and 4, and comparative compositions 1, 2, 3, 4 and 5, an average particle diameter of a polishing particle was measured immediately after preparation and after allowing to stand overnight (about 8 hours) to estimate stability of a particle of each composition. Micro Track UPA manufactured by NIKKISO Co., Ltd. was used for measuring an average particle diameter. TABLE 1 Comparative Comparative Comparative Comparative Comparative Composition Composition Composition Composition composition composition composition composition composition 1 2 3 4 1 2 3 4 5 Silica *¹ (% by 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 weight) Ammonium nitrate 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 (% by weight) Ammonium oxalate 0.04 (% by weight) Surfactant A *² 1.0 1.0 1.0 1.0 Surfactant B *³ 0.1 0.1 Surfactant C *⁴ 0.1 Surfactant D *⁵ 1.0 Surfactant E *⁶ 1.0 Surfactant F *⁷ 1.0 Ta film 520 640 520 580 520 — — 563 32 polishing rate (Å min) Film SiOC 99.5 99.4 99.4 99.4 99.3 — — 90.7 88.1 particle Cu 99.5 99.5 99.5 99.9 99.5 — — 92.1 90.5 removing Ta 99.5 99.5 99.5 99.9 99.5 — — 92.3 92.3 rate (%) Average particle 8 12 12 12 15 Not Not 8 8 diameter of determined determined polishing particle immediately after compounding (nm) Average particle 12 16 16 16 Not Not Not 12 8 diameter of determined determined determined polishing particle after allowing to stand overnight (nm)

[0091] All of the compositions 1 to 4 were able of polishing Ta at a high speed, have high particle removability on a low dielectric film after polishing, and hardly had adhered polishing abrasive. In addition, after preparation, precipitation did not occur, and stability for storing was excellent.

[0092] In addition, the composition 4 had extremely better particle removability on a metal film after polishing.

[0093] On the other hand, even in the case of using an anionic surfactant, in the composition using an anionic surfactant having only one anionic functional group as in the comparative composition 1, whereas a polishing rate and efficiency of washing were similar to the compositions 1 to 4, after preparation, polishing particles were aggregated, and an aggregate was precipitated, and thus, there was a problem on stability for storing. Also in the comparative compositions 2 and 3 using an anionic surfactant having one anionic functional group, polishing abrasive were aggregated, an aggregate was precipitated, and thus, the stability for storing is insufficient. In addition, in the comparative composition 4 containing no surfactant, since wettability between a low dielectric constant film is deteriorated, and the surface is immediately dried, efficiency of washing thereafter is insufficient, and in the comparative composition 5 containing no nitrate, a rate of polishing Ta was low.

[0094] According to the present invention, there can be provided a metal polishing composition which can polish a metal such as Cu and Ta at a high speed, has high efficiency of washing to a hydrophobic low dielectric constant film, and is excellent in stability for storing, and in which a polishing abrasive is not precipitated during storage. 

1. A metal polishing composition comprising an anionic surfactant having 2 or more anionic functional groups in a molecule, a polishing abrasive, an inorganic salt and water.
 2. The metal polishing composition according to claim 1, wherein the anionic surfactant is an anionic surfactant having further an ether linkage in a molecule.
 3. The metal polishing composition according to claim 1, wherein the anionic functional group is a functional group selected from the group consisting of a sulfonic acid group, a phosphonic acid group, a phosphoric acid group and a carboxylic acid group.
 4. The metal polishing composition according to claim 1, wherein the composition further contains a nonionic surfactant represented by the formula (I): Y—O—(C_(a)H_(2a)O)_(b)—(C_(x)H_(2x)O)_(y)Z  (I) (wherein a, b, x and y are independently a positive integer, and Y and Z are independently a hydrogen atom or a hydrocarbon group having a carbon number of 9 to 19).
 5. The metal polishing composition according to claim 4, wherein a is equal to x in the formula (I).
 6. The metal polishing composition according to claim 4, wherein the composition contains at least two nonionic surfactants represented by the formula (I).
 7. The metal polishing composition according to claim 6, wherein a is equal to x in at least one nonionic surfactant represented by the formula (I).
 8. The metal polishing composition according to claim 1, wherein the polishing abrasive is an inorganic particle.
 9. The metal polishing composition according to claim 8, wherein the inorganic particle is metal oxide.
 10. The metal polishing composition according to claim 9, wherein the metal oxide is silicon dioxide.
 11. The metal polishing composition according to claim 1, wherein the inorganic salt is a salt of an inorganic acid, and one selected from the group consisting of alkylammonium hydroxide, ammonia, alkylamine, alkanolamine and hydroxylamines.
 12. The metal polishing composition according to claim 11, wherein the inorganic acid is one selected from the group consisting of nitric acid, phosphoric acid, hydrochloric acid and sulfuric acid.
 13. The metal polishing composition according to claim 1, wherein the composition further contains an organic acid or a salt thereof.
 14. The metal polishing composition according to claim 9, wherein the organic acid or a salt thereof is at least one selected from the group consisting of acetic acid, citric acid, lactic acid, malonic acid, tartaric acid, succinic acid, oxalic acid, amino acid, and a salt thereof. 